﻿ Le Monde puzzle [#1110] – Data Science Austria

# Le Monde puzzle [#1110]

Want to share your content on R-bloggers? click here if you have a blog, or here if you don’t.  A low-key sorting problem as Le Monde current mathematical puzzle:

If the numbers from 1 to 67 are randomly permuted and if the sorting algorithm consists in picking a number i with a position higher than its rank i and moving it at the correct i-th position, what is the maximal number of steps to sort this set of integers when the selected integer is chosen optimaly?

As the question does not clearly state what happens to the number j that stood in the i-th position, I made the assumption that the entire sequence from position i to position n is moved one position upwards (rather than having i and j exchanged). In which case my intuition was that moving the smallest moveable number was optimal, resulting in the following R code

```sorite<-function(permu){ n=length(permu) p=0 while(max(abs(permu-(1:n)))>0){ j=min(permu[permu<(1:n)]) p=p+1 permu=unique(c(permu[(1:n)
```

which takes at most n-1 steps to reorder the sequence. I however checked this insertion sort was indeed the case through a recursive function

```resorite<-function(permu){ n=length(permu);p=0 while(max(abs(permu-(1:n)))>0){ j=cand=permu[permu<(1:n)] if (length(cand)==1){ p=p+1 permu=unique(c(permu[(1:n)
```

which did confirm my intuition.